The invention relates to the field of production and working of chemical fibers, and in particular the process of mechanical crimping, which consists in a plastic stress deformation of each single filament of a fiber bundle.
A crimped filament is identifiable by its wave-formed aspect, the number of waves being variable per unit of length depending on the future use of the product. Two crimped categories can be distinguished: a bidimensional type (with waves in a single filament belonging basically to a same plane) and tridimensional (with the waves being oriented in space). Bidimensional crimping is obtained through mechanical crimping machines, while tridimensional crimping is obtained by the action of pressurised fluids flowing through jets, or through thermal action (in dual component fibres, for example).
Conventional mechanical crimpers comprise a crimping chamber and employ a pair of opposed motorized rollers which squeeze the fiber bundle and thus cause it to deform by compressive and bending stress; the crimping chamber being formed by two cutters of a same length close to or contacting the rollers and two lateral walls flanking the rollers and the cutters.
Since contact between fiber bundle and thrust rollers occurs along a generatrix of the rollers, high specific pressures on the fiber are necessary, which reach 40 Kg for each mm length of the generatrix.
The crimping chamber exhibits an aperture on a side opposite to the rollers through which the processed fiber exits.
In mechanical crimpers of the above-described type, working at high speeds renders adhesion of the rollers to the fiber difficult to maintain, since inertia leads to the rollers' inadequately coping with variations in fiber thickness, so that discontinuous crimping occurs and the final bundles are of poor quality.
A further drawback i s that unexpected loss of incoming fiber tension leads to snaring and tangling.
Further, the rollers can damage each other as the usually low-denier fiber bundles do not keep them apart. This effect, known as hammering, increases progressively together with speed up until the external profiles of the rollers are permanently damaged, with resulting polygonal shapes that render their efficacy geometrically impossible. Also due to the low denier, any slight pinching of the fiber between the blades of the cutters and the rollers causes breaking of the fiber bundles and an ensuing tangle in the crimping chamber.
The main aim of the invention to obviate the above drawbacks and enable a high-velocity bidimensional crimping to be achieved.
To achieve the above, it is necessary to minimise the inertias, reducing specific pressures exerted on the fiber by the rollers, and to prevent fiber shavings from infiltrating between the point of the cutter and the rollers, by pushing in an opposite direction.